UV cutting filters for cameras are what try to block UV rays without influencing visible light or color properties of lenses at all. Accordingly, they are required to have light transmission characteristics changing drastically (sharply-cutting characteristics) in the boundary region between visible light and UV rays. And they are required also to have flat light transmission characteristics for visible light and to have excellent color rendering properties.
As a glass capable of absorbing and/or blocking UV rays, a glass containing cerium oxide is known (Patent Document 1). Cerium oxide has a strong absorption at about 310 nm, however, for obtaining a glass capable of absorbing the light of 350 nm or longer, a large amount of cerium oxide may be needed. A glass containing cerium oxide in a large amount may absorb visible light and may be colored in yellow or brown. Such a glass may block not only UV rays but also visible light, and is inferior in terms of properties of selectively-blocking-UV rays.
Therefore, plastic materials have been considered to be used in place of such a glass. For blocking UV rays by plastic materials, the method of adding any organic ultraviolet absorber such as benzotriazole-series, benzophenone-series and salicylic acid-series compounds to plastic materials is known (see Patent Document 2). However, many of thermoplastic resins added with any low-molecular ultraviolet absorber may suffer from volatilization and the mold-deposit problem when they are subjected to a forming process at a high temperature.
There is another problem that conventional UV-cut materials suffer from lacking sharpness of changing the light transmission characteristics in the boundary region between visible light and UV rays. And the thickness of the conventional UV-cut filter lens is not so thin that it doesn't have sufficient transmission for the visible light, sufficient flat light transmission characteristics for visible light, and excellent color rendering properties.
As a method for improving fluidity, adding a dihydroanthracene compound to polycarbonate resins is known (Patent Document 3). However, any optical properties such as absorbance distribution are not described. Although polycarbonate resins having an anthracene skeleton in the main chain are proposed (Patent Document 4), they are poor in terms of light resistance, and can not be used as an optical material.